1. Field of the Invention
The present invention relates to a three-dimensional measuring instrument, an image pickup apparatus and a method for adjusting the image pickup apparatus, and more specifically concerns a technique that is used for an image pickup apparatus including a plurality of cameras and a three-dimensional measuring instrument so as to adjust the positions of the cameras and the optical axis directions thereof.
2. Description of the Related Art
Conventionally, a “stereo method”, which obtains three-dimensional shape information and distance information to a measuring subject by using two picked-up images obtained by capturing images of the measuring subject from two mutually different positions, has been known. In this stereo method, by utilizing an image-formation positional deviation (parallax error) of a measuring subject occurring between two picked-up images, a depth distance is calculated based upon the principle of triangular survey.
For example, Japanese Patent Application Laid-Open No. 2006-250889 has disclosed a three-dimensional measuring system that adopts the stereo method. In this Patent Application, the three-dimensional measuring system including two cameras has been disclosed.
Image inspection systems utilizing the stereo method have been utilized in various fields. As a typical field of application of this image inspection system, a product inspection process in a production line of a factory is exemplified.
Most of the image inspection systems that have been conventionally introduced to production lines of factories have a small camera viewing field, with a short working distance (distance from the front face of a lens to a work). Consequently, upon introducing an image inspection system to a production line, the user can carry out adjustments in the positional relationship between the work and the camera viewing field or adjustments of the working distance comparatively easily.
In recent years, however, there have been strong demands for applications of an image inspection system to industrial products having a large size. In the case of large-size products requiring complicated assembling operations, there is a high possibility that operations to be carried out by the man and operations to be carried out by the machine are mixed in a production line. Therefore, upon installing a camera for use in an image inspection system in the production line, the camera needs to be set apart from the products so as not to intervene with the transferring processes and assembling processes of the product (that is, the work). For this reason, the working distance of the camera is inevitably made longer.
When the working distance of the camera is made longer, even a slight change in the light axis direction of the camera causes a large shift of the camera viewing field. Consequently, when the user adjusts the camera optical axis direction so as to capture an image of a predetermined inspection area on the work, the time required for the adjustments tends to become longer.
Moreover, in the above-mentioned three-dimensional measuring system, viewing fields of a plurality of cameras need to be superposed with one another. Consequently, in the case of the three-dimensional measuring system, the adjustments of the viewing fields of the cameras tend to become difficult as the working distance of the cameras becomes longer.
The present invention has been devised to solve the above-mentioned problems, and its objective is to provide easier adjustments of the positions and the viewing fields of the cameras in an image pickup apparatus provided with a plurality of cameras.